Improving results in rat fracture models: enhancing the efficacy of biomechanical testing by a modification of the experimental setup.

BACKGROUND: Animal fracture models, primarily performed in rats, are crucial to investigate normal and pathological bone healing. However, results of biomechanical testing representing a major outcome measure show high standard deviations often precluding statistical significance. Therefore, the aim of our study was a systematical examination of biomechanical characteristics of rat femurs during three-point bending. Furthermore, we tried to reduce variation of results by individually adapting the span of bearing and loading areas to the bone's length. METHODS: We examined 40 paired femurs of male Wistar-rats by DXA (BMD and BMC of the whole femur) and pQCT-scans at the levels of bearing and loading areas of the subsequent biomechanical three-point bending test. Individual adjustment of bearing and loading bars was done respecting the length of each specimen. Subgroups of light (< 400 g, n = 22) and heavy (> 400 g, n = 18) animals were formed and analysed separately. We furthermore compared the results of the individualised bending-setting to 20 femurs tested with a fix span of 15 mm. RESULTS: Femurs showed a length range of 34 to 46 mm. The failure loads ranged from 116 to 251 N (mean 175.4 ± 45.2 N; heavy animals mean 221 ± 18.9 N; light animals mean 138.1 ± 16.4 N) and stiffness ranged from 185 N/mm to 426 N/mm (mean 315.6 ± 63 N/mm; heavy animals mean 358.1 ± 34.64 N/mm; light animals mean 280.8 ± 59.85 N/mm). The correlation of densitometric techniques and failure loads was high (DXA R2 = 0.89 and pQCT R2 = 0.88). In comparison to femurs tested with a fix span, individual adaptation of biomechanical testing homogenized our data significantly. Most notably, the standard deviation of failure loads (221 ± 18.95 N individualized setting vs. 205.5 ± 30.36 N fixed) and stiffness (358.1 ± 34.64 N/mm individualized setting vs. 498.5 ± 104.8 N/mm fixed) was reduced by at least one third. CONCLUSIONS: Total variation observed in any trait reflects biological and methodological variation. Precision of the method hence affects the statistical power of the study. By simply adapting the setting of the biomechanical testing, interindividual variation could be reduced, which improves the precision of the method significantly.

Whole bone testing in small animals: systematic characterization of the mechanical properties of different rodent bones available for rat fracture models.

OBJECTIVES: Rat fracture models are extensively used to characterize normal and pathological bone healing. Despite, systematic research on inter- and intra-individual differences of common rat bones examined is surprisingly not available. Thus, we studied the biomechanical behaviour and radiological characteristics of the humerus, the tibia and the femur of the male Wistar rat-all of which are potentially available in the experimental situation-to identify useful or detrimental biomechanical properties of each bone and to facilitate sample size calculations. METHODS: 40 paired femura, tibiae and humeri of male Wistar rats (10-38 weeks, weight between 240 and 720 g) were analysed by DXA, pQCT scan and three-point-bending. Bearing and loading bars of the biomechanical setup were adapted percentually to the bone's length. Subgroups of light (skeletal immature) rats under 400 g (N = 11, 22 specimens of each bone) and heavy (mature) rats over 400 g (N = 9, 18 specimens of each bone) were formed and evaluated separately. RESULTS: Radiologically, neither significant differences between left and right bones, nor a specific side preference was evident. Mean side differences of the BMC were relatively small (1-3% measured by DXA and 2.5-5% by pQCT). Over all, bone mineral content (BMC) assessed by DXA and pQCT (TOT CNT, CORT CNT) showed high correlations between each other (BMC vs. TOT and CORT CNT: R2 = 0.94-0.99). The load-displacement diagram showed a typical, reproducible curve for each type of bone. Tibiae were the longest bones (mean 41.8 ± 4.12 mm) followed by femurs (mean 38.9 ± 4.12 mm) and humeri (mean 29.88 ± 3.33 mm). Failure loads and stiffness ranged from 175.4 ± 45.23 N / 315.6 ± 63.00 N/mm for the femurs, 124.6 ± 41.13 N / 260.5 ± 59.97 N/mm for the humeri to 117.1 ± 33.94 N / 143.8 ± 36.99 N/mm for the tibiae. Smallest interindividual differences were observed in failure loads of the femurs (CV% 8.6) and tibiae (CV% 10.7) of heavy animals, light animals showed good consistency in failure loads of the humeri (CV% 7.7). Most consistent results of both sides (left vs. right) in failure loads were provided by the femurs of light animals (mean difference 4.0 ± 2.8%); concerning stiffness, humeri of heavy animals were most consistent (mean difference of 6.2 ± 5%). In general, the failure loads showed strong correlations to the BMC (R2 = 0.85-0.88) whereas stiffness correlated only moderate, except for the humerus (BMC vs. stiffness: R2 = 0.79). DISCUSSION: Altogether, the rat's femur of mature specimens showed the most accurate and consistent radiological and biomechanical results. In synopsis with the common experimental use enabling comparison among different studies, this bone offers ideal biomechanical conditions for three point bending experiments. This can be explained by the combination of a superior aspect ratio and a round and long, straight morphology, which satisfies the beam criteria more than other bones tested.

Mechanical torque measurement in the proximal femur correlates to failure load and bone mineral density ex vivo.

Knowledge of local bone quality is essential for surgeons to determine operation techniques. A device for intraoperative measurement of local bone quality has been developed by the AO-Research Foundation (Densi - Probe®). We used this device to experimentally measure peak breakaway torque of trabecular bone in the proximal femur and correlated this with local bone mineral density (BMD) and failure load. Bone mineral density of 160 cadaver femurs was measured by ex situ dualenergy X-ray absorptiometry. The failure load of all femurs was analyzed by side-impact analysis. Femur fractures were fixed and mechanical peak torque was measured with the DensiProbe® device. Correlation was calculated whereas correlation coefficient and significance was calculated by Fisher's Ztransformation. Moreover, linear regression analysis was carried out. The unpaired Student's t-test was used to assess the significance of differences. The Ward triangle region had the lowest BMD with 0.511 g/cm(2) (±0.17 g/cm(2)), followed by the upper neck region with 0.546 g/cm(2) (±0.16 g/cm(2)), trochanteric region with 0.685 g/cm(2) (±0.19 g/cm(2)) and the femoral neck with 0.813 g/cm(2) (±0.2 g/cm(2)). Peak torque of DensiProbe® in the femoral head was 3.48 Nm (±2.34 Nm). Load to failure was 4050.2 N (±1586.7 N). The highest correlation of peak torque measured by Densi Probe® and load to failure was found in the femoral neck (r=0.64, P<0.001). The overall correlation of mechanical peak torque with T-score was r=0.60 (P<0.001). A correlation was found between mechanical peak torque, load to failure of bone and BMD in vitro. Trabecular strength of bone and bone mineral density are different aspects of bone strength, but a correlation was found between them. Mechanical peak torque as measured may contribute additional information about bone strength, especially in the perioperative testing.

Acute osteomyelitis of the humerus mimicking malignancy: Streptococcus pneumoniae as exceptional pathogen in an immunocompetent adult.

BACKGROUND: Chronic osteomyelitis due to direct bone trauma or vascular insufficiency is a frequent problem in orthopaedic surgery. In contrast, acute haematogenous osteomyelitis represents a rare entity that almost exclusively affects prepubescent children or immunodeficient adults. CASE PRESENTATION: In this article, we report the case of acute pneumococcal osteomyelitis of the humerus in an immunocompetent and otherwise healthy 44-year-old male patient presenting with minor inflammation signs and misleading clinical features. CONCLUSIONS: The diagnosis had to be confirmed by open biopsy which allowed the initiation of a targeted therapy. A case of pneumococcal osteomyelitis of a long bone, lacking predisposing factors or trauma, is unique in adults and has not been reported previously.

Polypropylene meshes coated with a polysaccharide based bioadhesive for intra-abdominal mesh fixation in a rabbit model.

BACKGROUND: In this study, we evaluate a new bioadhesive for intra-abdominal onlay mesh fixation of a polypropylene-polyvinylchloride graft. METHODS: Three pieces of a commercially available polypropylene/polyvinylfluoride mesh, each 3 × 3 cm in size, and three pieces of the same mesh coated with a polysaccharide bioadhesive were fixated to the surface of the anterior abdominal wall of 30 New Zealand white rabbits. The fixation was performed either by using four transabdominal Prolene(®) 4/0 sutures, four spiral tacks (Protack 5 mm Tyco), or cyanoacrylate glue (Glubran(®) GEM, Viareggio, Italy). Each mesh position and the according kind of fixation were randomized before implantation. The animals were sacrificed 12 weeks postoperatively. After determining the extent of intra-abdominal adhesions, the meshes were excised en bloc with the anterior abdominal wall for tensile strength measurements and histological analysis. RESULTS: All meshes coated with the bioadhesive adhered to the intact peritoneum without extra fixation. Irrespective of the fixation technique coated meshes led to more and stronger adhesions. Mesh shrinkage by scarring was increased in coated meshes fixed with glue and low in uncoated meshes fixed with tacks. Testing the tensile strength, coated meshes fixed with transfascial sutures achieved the best results (16.14 ± 6.1 N), whereas coated meshes fixed with glue showed the lowest strength (10.39 ± 4.81 N). The foreign body reaction was considerably more distinctive using coated mesh. The mesh ingrowth was not influenced by this reaction. CONCLUSIONS: All meshes coated with the new bioadhesive were self-adhesive in that way; they stayed in position when attached to the peritoneum. Although this may facilitate intra-operative mesh fixation, the bioadhesive displayed several disadvantages, such as stronger adhesions and an increased shrinkage of the implant. The tensile strength was not influenced by the use of the bioadhesive. At present, we see no major advantage for polysaccharide bioadhesive applied in this study.

Lower limb alignment in the frontal plane: analysis from long standing radiographs and computer tomography scout views: an experimental study.

OBJECTIVES: A profound knowledge of physiologic lower limb alignment is essential to understand deformities and to plan surgical correction. The gold standard in radiographic assessment is the long standing radiograph with a forward directed patella. The advantage of computed tomography (CT) is that its cutting-edge image technique can visualize the femur condyles. Study purpose was to determine if the CT-scout view has the potential to replace the standing radiograph. MATERIALS AND METHODS: We compared the geometric data obtained from long standing radiograph and CT-scout views both with patella forward position. Furthermore, we developed a method of positioning the lower extremity stable on the CT table, where the femoral condyles became the new orientation criterion. Finally, we evaluated differences in the data ascertainment between the long standing radiograph with patella facing forward and the CT-scout view with the posterior edge of femoral condyles orientated parallel to the radiographic cassette. RESULTS: The geometric data of long standing radiograph and CT-scout views are comparable if the leg is in the same rotational position. We developed a CT positioning jig to adjust the femur condyles parallel to the radiographic cassette. In 80 % of the cases, the deviation was 5° or less. These scout views showed statistically significant differences when compared with data from standing radiograph with a forward centered patella. CONCLUSION: No evidence was found clearly excluding the possibility of an exclusive use of the CT-scout view for the analysis of the leg geometry. However, advantages of the long standing radiograph became obvious.

Nontraumatic subluxation of the atlanto-axial joint as rare form of acquired torticollis: diagnosis and clinical features of the Grisel's syndrome.

STUDY DESIGN: Case report and review of the literature. OBJECTIVE: We report a case of Grisel's syndrome with a delayed diagnosis. The patient's first presentation in our pediatric orthopedics department was 2 month after surgery (cochlea implantation) with a persistent torticollis. Radiographs revealed a subluxated atlantoaxial joint. We treated our patient with manual repositioning and calculated antibiotics, which lead to a restitutio ad integrum within a short time. SUMMARY OF BACKGROUND DATA: Grisel's syndrome is synonymous with rare nontraumatic, rotational subluxation of the atlantoaxial joint (C1-C2). All formerly reported cases showed a clear association to infection or were related to head and neck surgery. Still, there is a lack of understanding about pathogenetic features and causative agents. In 1977 Fielding proposed a classification of the atlantoaxial subluxation and stage-related therapy was recommended. METHODS: Our patient was a 11-year-old girl with a torticollis after insertion of a cochlea implant. After surgery, physiotherapy was performed because of her wryneck. As the symptoms did not improve, she was presented in our clinic. Our radiographs revealed a subluxated atlantoaxial joint. RESULTS: In general anesthesia we performed a manual repositioning and she was temporarily immobilized with a cervical collar for 2 weeks. In addition, we administered calculated antibiotics, although CRP and leukocytes were not elevated. The follow up showed a good repositioning within a short time. CONCLUSION: At least in this case, our treatment led to shorter recovery and avoidance of halo fixation. Our new therapeutic approach to patients with Grisel's syndrome might lead to a shorter recovery.

Cyanoacrylate glue for intra-abdominal mesh fixation of polypropylene-polyvinylidene fluoride meshes in a rabbit model.

BACKGROUND: Cyanoacrylate glues are tissue adhesive with high adherent and hemostatic properties. The aim of this study was to evaluate the efficacy of cyanoacrylates glue for polypropylene-polyvinylidene fluoride (PP-PVDF) intraperitoneal onlay mesh (IPOM) fixation in a rabbit model. MATERIALS AND METHODS: In 40 New Zealand white rabbits, three pieces (3×3cm) of a PP-PVDF mesh (n=120) were fixed in IPOM technique on both sides of a midline laparotomy. For mesh fixation we used spiral tacks, nonabsorbable sutures, or cyanoacrylate glue in a randomized manner. All animals were killed after 12 wk. The prosthetic materials were excised en bloc with the anterior abdominal wall for evaluation of the tensile strength and histologic analysis. Results are presented as mean and standard deviation. RESULTS: Meshes fixed with glue showed a significantly higher tenacity of adhesions (2.75±0.97) compared with those with tacks (2.44±0.97 sutures versus 1.91±0.92 tacks). The percentage of adhesions in the glue group was comparable to the suture group (36.50% ± 27.60% glue, 37.62% ± 27.36% suture). The tensile strength of stapled and sutured meshes was significantly higher than the tensile strength glued mesh (14.15±0.97N suture versus 14.84±0.74 stapler versus 9.64±0.78N glue). Mesh shrinkage was irrespective of the fixation technique. The inflammation reaction was more pronounced in the glue group. CONCLUSIONS: Although cyanoacrylate glue showed a considerable cellular ingrowth in this rabbit model, sutures and tacks proved to be superior for IPOM fixation of PP-PVDF meshes in terms of tensile strength.

Prediction of the fracture load of whole proximal femur specimens by topological analysis of the mineral distribution in DXA-scan images.

OBJECTIVE: To evaluate scanner-generated images of hip specimens obtained from dual energy X-ray absorptiometry (DXA) by quantitative image analysis of bone mineral distribution in the standard regions of interest (ROI), to predict the ultimate mechanical strength, and to compare the predictive potential with standard densitometry. MATERIALS AND METHODS: Femoral bone mineral density (BMD) of 100 hip specimens was obtained by DXA in the total hip, shaft, trochanteric, and neck ROI. Maximum compressive strength (MCS) of the specimens was measured in a mechanical loading device simulating a fall on the greater trochanter. The topology of bone mineral distribution in the scan images was evaluated by image processing methods based on the Minkowski functionals (MF) using the optimized topological parameter MF2D. Correlation and multivariate analysis were employed to assess the statistical potential of BMD and MF2D with respect to predict the mechanical strength of the femur specimens. RESULTS: R2 for the correlation between load-to-failure and BMD varied between 0.73 and 0.79 (exponential curve fit, p<0.001), being highest in the trochanteric ROI. Correlation between load-to-failure of the specimens with the topological parameter MF2D ranged from R2 =0.8 to 0.91 (p<0.001). In a multivariate model combining the topological information from all ROIs, correlation with MCS rose to R2 =0.94. CONCLUSION: The topological parameter MF2D can be employed to predict the mechanical strength of proximal femur specimens from DXA-generated images. Performance is superior to standard evaluation of DXA. In the future, the proposed image processing method may serve to improve the assessment of an individual's fracture risk.

Thoracic Outlet Syndrome Caused by a Pseudoaneurysm After Pseudarthrosis of the Clavicle.

Clavicle fractures are common, with the majority treated conservatively. If treated conservatively, pseudarthrosis of the clavicle is reported in up to 3% of the cases. In rare cases, pseudarthrosis of the clavicle may cause pseudoaneurysm formation, resulting in compression of the brachial plexus and the adjoining vessels, which may produce neurological symptoms and circulatory disorders. Here, we describe two cases of the late onset of pseudoaneurysm formation after pseudarthrosis of the clavicle. Both cases were remarkable because they showed clinical symptoms of TOS. Therefore, surgical treatment was performed and included claviculectomy, resection of the pseudoaneurysm and interposition grafting with an artificial prosthesis. One year after the operation, both patients showed excellent upper extremity function without any deficit of vascular, sensorial or motorial function. Patient's history and radiological findings are the keys to diagnosis. Without treatment, the prognosis is poor with spontaneous development of bleeding or gangrene. Therefore, surgical treatment has to be performed, especially when neurological symptoms occur.

Double tube stent-grafts for infrarenal aortic aneurysm: a new concept.

PURPOSE: To present the concept of double tube stent-grafts and examine the indications for and results achieved with these devices. METHODS: From January 1, 2000, to December 31, 2005, 759 patients who underwent endovascular repair of infrarenal aortic aneurysms at 2 centers. Of these, 45 (5.9%) patients received a double tube stent-graft; complete operative and follow-up data were available for retrospective analysis in 41 patients (33 men; mean age 73.1+/-8.9 years). Diameters measured before stent-graft implantation and at follow-up (12, 24, 36, and 48 months) with clinical examination, 2-phase computed tomographic angiography, duplex sonography, and biplanar abdominal radiography were tested for significant changes using ANOVA with the Bonferroni-Dunn correction. Late outcomes (clinical success and endoleak) were analyzed by the Kaplan-Meier method. RESULTS: The postoperative complication rate was 12.2%, with 2.4% systemic complications (1 patient with angina pectoris); the early mortality rate was 0%. Mean follow-up was 21.9+/-12.8 months (range 12-61) for the 41 patients. Four (9.8%) patients died during follow-up of cardiac causes (n = 2), lung cancer (n = 1), and bowel ischemia (n = 1). Four (9.8%) endoleaks were observed during follow-up: 1 distal type I, 2 type II, and 1 type III. Maximum aneurysm diameters shrank from 52.0+/-9.5 mm preoperatively to 44.0+/-10.9 mm (p<0.0001) postoperatively at the latest available follow-up. CONCLUSION: Our study supports the use of this double tube technique for repair of appropriate saccular infrarenal aortic aneurysms. The double tube stent-graft method appears safe in terms of endoleaks and migration, so we recommend that it be considered an option of endovascular aortic aneurysm therapy.

Quantitative scanning acoustic microscopy compared to microradiography for assessment of new bone formation.

Recently, it has been shown that quantitative scanning acoustic microscopy (SAM) is a powerful tool to image the acoustic impedance of even inhomogeneous materials like bone. Therefore, the aim of our study was to compare SAM to conventional microradiography with respect to histomorphometrical assessment of undecalcified sections of newly formed bone. Forty specimens were harvested 12 weeks after implantation of either autogenous cancellous bone graft or 5.0 mg of Osteogenic Protein-1 (BMP-7) in a critical-sized defect model in sheep. Undecalcified transverse bone sections of 500 microm thickness were investigated with conventional microradiography and SAM. Linear regression analysis was carried out to compare the measurements of the area of new bone formation within the defect sites. Both methods allowed for good discrimination between newly formed bone and cortical bone at the edges of the former defect. Images obtained with SAM revealed a better resolution and sharpness compared to that of microradiographs since SAM imaging unlike microradiography does not depend on the thickness of bone sections. The results of quantitative histomorphometric analysis obtained by both methods showed no significant differences, and it was possible to predict 90% of the variability of each method (coefficient of determination r2 = 0.90; P < 0.0001). In conclusion, SAM offers comparable quantitative histomorphometric information with a better spatial resolution than conventional microradiography. Thus, SAM is a promising new micro-visualizing technique for basic bone research.

Results of perioperative measurements of ankle-brachial index in popliteal artery entrapment syndrome.

OBJECTIVE: The purpose of this study was to demonstrate whether there is postoperative improvement in blood flow in the affected limb after surgical decompression in popliteal artery entrapment syndrome (PAES). For this purpose, the simple method of measuring Doppler ankle pressure with and without provocation was used preoperatively and postoperatively. PATIENTS AND METHODS: Doppler ankle pressure was measured preoperatively and postoperatively in neutral position (n=32) and with provocation (forced plantar flexion of the foot; n=32) in 32 limbs in 23 patients with PAES (19 men, 4 women; average age, 38.24 +/- 12.25 years) operated on between January 1, 1986, and December 31, 2000. The reference method was angiography with provocation in 18 patients and duplex ultrasound scanning in 14 patients. RESULTS: Patients were assigned to one of two groups (A and B) on the basis of ankle-brachial index (ABI) at rest. Group A (mean age, 38.19 +/- 11.60 years) included all limbs (n=24) with ABI>0.9 preoperatively, and group B (mean age, 42.39 +/- 14.38 years) comprised all limbs (n=8) with ABI<0.9. Improvement in ABI under provocation after operation (group A, P<.0001; group B, P<.0004) was highly significant. In group B there was also a highly significant difference in ABI in the neutral position before and after operation (P=.0044); this could not be demonstrated in group A. Angiography or duplex sonography postoperatively did not provide any additional information. CONCLUSION: Our results indicate that determination of ABI alone, with and without provocation, is sufficient as a postoperative follow-up examination to appraise decompression and for quality assurance of PAES. Compared with other more elaborate instrumental methods, measurement of ABI is relatively noninvasive, quick and easy to carry out, effective, and inexpensive.